Add support for keyup

Unless I'm missing something there appears to be no support for keyup, only keydown for hot keys.  PTHotKey implements all the hard stuff except the private _hotKeyUp method does nothing and offers no way to supply an action to call on key up.

This change completes keyUp support, adds a keyUpAction to PTHotKey, and adds an additional convenience class method for creating a hot key and supplying a keyUp action.